1. Field of the Invention
The present invention relates to an exposure apparatus or aligner and an exposure process, and in particular, to those in which an image of a pattern formed on an original body or a mask is exposure-transferred onto an exposure body or a substrate by scan-exposing the mask and the substrate through a mirror projection optical system while moving the mask and the substrate as a unit relative to the mirror projection optical system. Further in particular, the present invention also relates to an exposure apparatus and an exposure process for producing a liquid crystal display panel, especially, a large-sized liquid crystal display panel.
2. Related Background Art
A full wafer or one-shot exposure apparatus in which an image of a pattern formed on a mask is exposure-transferred onto a substrate by scan-exposing the mask and the substrate through a mirror projection optical system while moving the mask and the substrate as a unit relative to the mirror projection optical system has been used as an exposure apparatus to be used for producing a liquid crystal display panel, in particular, a liquid crystal display panel of a size of about 10 inches which expected to be widely utilized for small scale or personal computers. This is because such a type of exposure apparatus has a good resolution and a high productivity.
In this exposure apparatus, there is provided a well-known projection system containing three mirrors which have surfaces ground to a very high precision, and the mask and the substrate are scan-exposed as a unit relative to the projection system so that an entire image of the pattern on the mask is transferred onto the substrate using a good image area of an arcuate slit shape obtained by the projection system. In this apparatus, the size of an exposure area in a scanning direction (Y direction) is determined by a distance by which the mask and the substrate are scanned relative to the projection system, while that in a direction (X direction) orthogonal to the scanning direction is determined by a width in the X direction of the arcuate slit imaged by the mirror projection system.
On the other hand, the crystal liquid display panel has been produced as follows: The pattern on the mask is transferred onto a photoresist on the substrate, and processes similar to those for producing semiconductor devices such as IC's and LSI's are performed. The substrate is used as a pixel driving circuit for controlling the drive of the liquid crystal.
In the exposure apparatus for producing liquid crystal display panels, a necessary exposure area for producing the liquid crystal display panel will theoretically suffice if this exposure area has a size that covers a pixel pattern portion of the display panel and an electrode pattern portion provided on its periphery. In a large-sized substrate, however, a substrate having a size larger than an exposure area needed to expose a portion which will become a liquid crystal display panel is generally needed since a resist coating uniformity at the substrate periphery is low.
At present, the following is about to become a standard. That is, two liquid crystal display panels having a size of about 10 inches are taken from a large substrate of 320 mm.times.400 mm. However, the following disadvantages have arisen when only the liquid crystal panel portion is exposed using such a large substrate.
Normally, when a substrate is exposed for producing a liquid crystal display panel, a positive resist is used. Therefore, resist layers are layered on a periphery of the substrate each time one process or layer is performed unless a light beam is applied to the periphery. When the substrate is supplied from and to a transport cassette in the exposure apparatus, the layered resist layers are brought into engagement with a slot portion of the cassette to be peeled off. Thus, the peeled resist becomes dust. Further, the resist also becomes dust when the substrate is scribed. If a pattern transfer is performed with the dust on the substrate surface (the side on which the photoresist is coated), the yield of the liquid crystal panel extremely decreases.
In order to solve this problem, a light beam needs to be applied only to the photoresist on the periphery of the liquid crystal display panel on the substrate so as not to cause the resist layer to be layered thereon. Conventionally, the fabrication of liquid crystal display panels has been conducted in the following manner. While only a liquid crystal display panel portion requiring a considerable resolution is exposed using the above-discussed mirror projection type exposure apparatus or a well-known lens projection type exposure apparatus, its periphery is exposed using a proximity exposure apparatus which does not have a resolution needed to expose the liquid crystal display panel but is capable of exposing a large image field en bloc.
In a case wherein the periphery is exposed by another exposure apparatus, however, two exposure processes have to be conducted by two kinds of exposure apparatuses, respectively, when one-process (layer) patterning is to be performed on a substrate. As a result, the productivity is greatly lowered.
On the other hand, when considering that the exposure of the periphery is also conducted by the exposure apparatus that exposes the liquid crystal panel, portion, such exposure is possible by extending a scanning distance with respect to a londitudinal or Y direction in the mirror projection exposure apparatus. With respect to a lateral or X direction, such exposure becomes possible by expanding the width of an arcuate slit determined by the mirror projection optical system.
The extension of the scanning distance by which the mask and substrate are moved as a unit can readily be achieved only by extending a scanning guide for guiding the movement of the mask and substrate. The expansion of the width of the arcuate slit in the lateral direction, however, is quite difficult, if not impossible. In the following are reasons therefore.
1. The width of the arcuate slit needs to have a length that is capable of effectively exposing a liquid crystal display panel having a desired size. For example, the width should be set to about 280 mm in the exposure apparatus for producing a panel having a size of 10 inches. When the width of the arcuate slit is extended to 320 mm which is a lateral length of the substrate, the area of the slit is enlarged and hence an illumination light or exposure light for transferring the pattern will be diffused on the substrate. As a result, the illuminance on the substrate is reduced, and an exposure time during which the liquid crystal display panel portion is exposed is prolonged, leading to a low productivity.
2. When the width of the slit is expanded, the mirror projection optical system is enlarged in size and hence its working becomes difficult. Further, the size of the exposure apparatus is made large, and a wide foot space therefor is needed. A large exposure apparatus is undesirable because the exposure apparatus for producing the liquid crystal display panel is usually installed in a clean room similar to that for producing semiconductor devices.